Field of the Invention
The invention relates to a projection apparatus, and particularly relates to a projection apparatus having a non-telecentric illumination system.
Description of Related Art
A general rear projection display product mainly adopts an optical engine to produce images and project the images on a screen. In order to achieve a higher resolution of the images projected on the screen by the optical engine, a technical means adopted by the rear projection display product of the existing technique is to dispose a transparent plate on a transmission path of an image beam of the rear projection display product, and control the transparent plate to vibrate back and forth in an angle within a frame period. Therefore, when the image beam coming from an imaging device is transmitted to the transparent plate, a transmission direction of the image beam can be changed along with the vibration of the transparent plate and switched within the frame period. Then, the image beam passing through the transparent plate is projected to the screen through a lens. When the transparent plate is not deflected to the angle, the image beam is projected to a predetermined position on the screen by the lens, and when the transparent plate is deflected to the angle, the deflected image beam is projected to another predetermined position on the screen through the lens, where the two positions are partially overlapped. Since the transmission direction of the image beam is changed by the transparent plate, a user may view images of different positions on the screen produced by the image beam within the frame period. An image resolution of the imaging device of the rear projection display product of the existing technique is, for example, 2720×1530, and through superposition of images of different positions within the frame period, the image projected on the screen may achieve a resolution effect of 4K (3846×2163).
However, the rear projection display product of the existing technique still has following disadvantages. For example, the image beam incident to the lens from a place adjacent to an optical axis of the lens is referred to as a chief beam, and the image beam incident to the lens from a place away from the optical axis of the lens is referred to as an off-axis beam. An incident angle of the off-axis beam incident to the lens is greater than an incident angle of the chief beam incident to the lens. In other words, the incident angle of the image beam is different at different places of the lens. Therefore, when the transparent plate is deflected to an angle, a part of the image formed by the off-axis beam is deviated from a part of the image formed by the chief beam due to a larger refraction degree, and a distortion phenomenon is produced at a boundary of the images. The distortion phenomenon may cause a poor image quality. Moreover, since an offset generally exists between the optical axis of the lens and the imaging device in the general rear projection display product, the aforementioned distortion phenomenon becomes more severe due to the offset.
The information disclosed in this “BACKGROUND OF THE INVENTION” section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Further, the information disclosed in the “BACKGROUND OF THE INVENTION” section does not mean that one or more problems to be resolved by one or more embodiments of the invention was acknowledged by a person of ordinary skill in the art.